There are many marking systems that transport paper or other media after the paper is marked in a marking step or steps. Some such marking systems include electrostatic marking systems, non-electrostatic marking systems and printers or any other system where paper or other flexible media or receiving sheets are transported internally to an output device, such as a finisher and compiler station or stations. These devices include those used for collecting or gathering printed sheets so that they may be formed into books, pamphlets, forms, sales literature, instruction books and manuals and the like.
These marking systems, as above noted, have finisher and compilers located at a site after the receiving sheets (paper) have been marked. A finisher is generally defined as an output device that has various post printer functions or options such as hole punching, corner stapling, edge stapling, sheet and set stacking, letter or tri-folding, Z-Folding, Bi-folding, signature booklet making, set binding [including thermal, tape and perfect binding], trimming, post process sheet insertion, saddle stitching, and others. The function of the Compiler is to produce accurately registered or edge aligned sets of sheets prior to subsequent Finishing operations.
The compiler often employs a compiling wall or tray where gravity and/or frictional drive elements are used to drive sheets (paper) against the registration or compiling wall for registration of the staple or bind edge of a paper set. If desirable, frictional drive elements such as belts, scuffer wheels, or paddle wheels, etc. may be used. Sheet counting is frequently used as a criterion to index the Compiler Drive element shaft as the compiled stack height increases, but it does not successfully comprehend curl build up or variations in the paper media thickness.
The compiling capacity and bind edge sheet registration of the paper can be compromised with moderate to severe curl on the sheets. The curl can be concave up or concave down and curl build-up generally progressively increases as the paper stack height grows. Excessive curling can cause poor set registration and possibly paper jams or sheet damage. It is observed that curling is more significant with higher stack heights (above—50 to 70 sheet sets with 20# letter LEF), the bind edge height builds up faster than the set thickness, the curl build up is progressive, increasing more rapidly as Stack Height grows. When clamped by the Staple Head, the set shingles and Stapled Set Registration is disturbed as the Bind Edge Curl is suppressed. Increased load on the Bind Edge Curl Suppressors would solve the problem; however, it would also require a dramatic increase in sheet Drive Force to overcome the frictional drag effects of this increased suppression force, eventually leading to the buckling of light weight media in the compiler tray. When the incoming paper is not in proper registration because of curl, as noted, this causes poor set registration prior to stapling and other finishing steps.